1. Field of the Invention
The present invention relates to a process and system for condensing a multi-component fluid, where the process and system are designed to provide a substantial increase in a heat transfer coefficient during condensation of multi-component fluids resulting in a drastic reduction in size and cost of heat exchangers need to condense such fluids.
More particularly, the present invention relates to a process and system for condensing a multi-component fluid, where the process and system are designed to provide a substantial increase in a heat transfer coefficient during condensation of multi-component fluids resulting in a drastic reduction in size and cost of heat exchange units need to condense the fluids and includes at least two heat transfer stages and at least one scrubber interconnected so that streams are split and mixed in such a way as to increase the heat transfer coefficient in each heat exchange unit.
2. Description of the Related Art
The condensation of multi-component working fluids is widely used in the chemical, petro-chemical, refrigeration and power industries. It is important to note that the efficacy of this process is substantially lower than the efficacy of condensation of pure, single component fluids. In the process of condensation of single component fluids, the only thermal resistance is the thermal resistance of the film of condensate that covers the cooling surface. The temperature of this film is the same as the temperature of the whole condensing stream and therefore the temperature difference across the film of condensate is equal to the temperature difference between the temperature of the condensing steam and the temperature of the cooling surface.
In distinction to the process of the condensation of single component fluid, the process of condensing multi-component fluids occurs at variable temperatures and includes distinct sub-processes which occur simultaneously. Condensation occurs on a cooling surface which is covered by a film of condensate. Vapor which is not yet condensed is absorbed by this the surface of this film of condensate. The remaining non-condensed, portion of vapor is cooled by the surface of the film of condensate. In turn, the film of condensate is cooled by the cooling surface. The entire stream of heat removed from the fluid is therefore passing though the film of condensate, whereas only a portion of this stream, i.e., heat released in phase change and sensible heat released in the cooling of the vapor, is transferred to the surface of the film. Therefore, there is always a temperature difference between the vapor and the film of condensate as well as a temperature difference between the film of condensate and the cooling surface.
If, in any cross-section of a heat exchanger, the vapor and liquid would be thoroughly mixed so that they would be in complete equilibrium, then the mixture of liquid and vapor would have a temperature which is referred to as a “mixed mean temperature”, hereafter referred to as tmm. It is clear that the temperature of the vapor t″ is always higher than tmm, whereas the temperature of the film t′ is always lower than tmm. As a result, the driving force for transferring beat through the film of condensate, i.e., temperature difference in between the film and cooling surface, is reduced and the heat transfer coefficient is reduced as well.
It is clear that in the initial stages of condensation, when the condensing stream consists mostly of vapor, the temperature of the film of condensate is substantially lower than tmm, whereas the temperature of the vapor t″ is close to tmm. As a consequence of the temperature difference ΔT across the film is substantially reduced and the heat transfer coefficient is drastically reduced. On the contrary, in the final stages of condensation, where the greater part of stream is already in the form of a condensate, the temperature of the condensate t′ is close to tmm whereas the temperature of the vapor is substantially higher than tmm. In this case, the temperature difference Δt across the film and the heat transfer coefficient are only insignificantly reduced as compared to the condensation of single component fluids.
Thus, there is a need in the art for an apparatus and method using the apparatus for condensing a multi-component fluid while maximizing the heat transfer coefficient during the entire condensing process.